1. Field of the Invention
The present invention relates to a magnetic head for perpendicular magnetic recording for use to write data on a recording medium by means of a perpendicular magnetic recording system.
2. Description of the Related Art
The recording systems of magnetic read/write apparatuses include a longitudinal magnetic recording system in which the magnetization of signals is directed along the plane of a recording medium (the longitudinal direction), and a perpendicular magnetic recording system in which the magnetization of signals is directed perpendicular to the plane of a recording medium. It is known that the perpendicular magnetic recording system is harder to be affected by thermal fluctuation of the recording medium and capable of providing higher linear recording density, compared with the longitudinal magnetic recording system.
Magnetic heads for perpendicular magnetic recording typically have, like those for longitudinal magnetic recording, a structure in which a read head unit having a magnetoresistive element (hereinafter, also referred to as MR element) for reading and a write head unit having an induction-type electromagnetic transducer for writing are stacked on a substrate. The write head unit includes a coil and a main pole. The main pole has an end face located in a medium facing surface facing a recording medium. The coil produces a magnetic field corresponding to data to be written on the recording medium. The main pole passes a magnetic flux corresponding to the magnetic field produced by the coil, and produces a write magnetic field from its end face.
A magnetic head for use in a magnetic disk drive such as a hard disk drive is typically provided in a slider. The slider has the medium facing surface. The medium facing surface has an air inflow end (a leading end) and an air outflow end (a trailing end). An airflow that comes from the air inflow end into the space between the medium facing surface and the recording medium causes the slider to slightly fly over the surface of the recording medium. The recording medium includes a magnetic recording layer. Tracks are concentrically formed in the magnetic recording layer. The tracks are the area of the magnetic recording layer on which data is to be written.
Here, the side of positions closer to a leading end relative to a reference position will be defined as the leading side, and the side of positions closer to a trailing end relative to the reference position will be defined as the trailing side. The leading side is the rear side in the direction of travel of the recording medium relative to the slider. The trailing side is the front side in the direction of travel of the recording medium relative to the slider.
The magnetic head is typically disposed near the trailing end of the medium facing surface of the slider. In a magnetic disk drive, positioning of the magnetic head is performed by a rotary actuator, for example. In this case, the magnetic head moves over the recording medium along a circular orbit about the center of rotation of the rotary actuator. In such a magnetic disk drive, a tilt of the magnetic head with respect to the tangent of the circular track, which is called a skew, occurs according to the position of the magnetic head across the tracks.
In particular, in a magnetic disk drive of the perpendicular magnetic recording system which is higher in capability of writing on a recording medium than the longitudinal magnetic recording system, the skew mentioned above can cause the phenomenon that signals already written on one or more tracks in the neighborhood of a track targeted for writing are erased or attenuated during writing of a signal on the track targeted for writing. In the present application, this phenomenon will be called unwanted erasure. Unwanted erasure includes adjacent track erasure (ATE) and wide-area track erasure (WATE). To achieve higher recording density, it is necessary to prevent unwanted erasure.
In order to prevent unwanted erasure induced by the skew and achieve higher recording density, it is effective to provide a write shield in the vicinity of the main pole. U.S. Pat. No. 8,867,168 B2 discloses a magnetic head with a write shield having an end face that is located in the medium facing surface and surrounds the end face of the main pole.
In a magnetic head including the write shield, there is typically provided a return path section for connecting the write shield to a part of the main pole located away from the medium facing surface. By providing such a return path section, a space is defined between the main pole, the return path section and the write shield, and a magnetic path is formed through the main pole, the return path section and the write shield. The coil passes through the aforementioned space, and produces a magnetic flux to pass through the aforementioned magnetic path. The main pole produces a write magnetic field in response to the magnetic flux.
Examples of coils for use in magnetic heads for perpendicular magnetic recording include a helical coil wound around a main pole, such as one disclosed in U.S. Pat. No. 8,867,168 B2.
Magnetic heads for perpendicular magnetic recording are increasing in frequency of write signals to achieve higher recording densities. Accordingly, it is demanded of magnetic heads for perpendicular magnetic recording that the rate of magnetization reversal of the main pole be increased.
In a conventional magnetic heads for perpendicular magnetic recording including the helical coil, the entire magnetic path passing through the main pole, the return path section and the write shield is driven by the helical coil. The magnetic path is relatively long. Further, the total volume of the main pole, the return path section and the write shield is relatively large. Accordingly, for the conventional magnetic heads for perpendicular magnetic recording, increasing the rate of magnetization reversal of the main pole is difficult with a helical coil that is small in the number of turns and magnetomotive force. Even if the number of turns of the helical coil is increased to produce a greater magnetomotive force, increasing the rate of magnetization reversal of the main pole is still difficult because the increase in the number of turns makes the aforementioned magnetic path longer and increases the total volume of the main pole, the return path section and the write shield.